1. Field of the Invention
The present invention relates to suspensions of mineral fillers, preferably calcium carbonates, and more preferably ground fillers, for example ground calcium carbonates, and additives for producing such suspensions, for example grinding aid agents. The grinding aid agents of the present invention provide suspensions of fillers with improved mechanical properties, particularly the properties of “strength at young ages” of cement matrices or hydraulic binders, or more particularly hydraulic concretes, prepared with these suspensions.
The present invention also relates to mortars, concretes and other compositions based on cement and/or semi-hydrate calcium sulphate, i.e., hydraulic compounds or binders.
2. Discussion of the Background
It is known that cement matrices such as concretes, mortars, grouts, etc, more particularly hydraulic concretes, are used in two main applications: ready-for-use concretes and prefabricated products. In addition, it is known that concrete is composed essentially of a cement and an aggregate as well as water and admixtures or additives.
By granulometry, aggregates are classified into several categories known to those skilled in the art, and defined by the French standard XP P 18-540.
In this standard, the families of aggregates comprise:                0/D fillers, where D<2 mm, and at least 70% of the aggregate passes through a 0.063 mm screen,        0/D fine sands, where D≦1 mm, and less than 70% of the aggregate passes through a 0.063 mm screen,        0/D sands, where 1<D≦6.3 mm,        gravels, where D>6.3 mm,        d/D fine gravels, where d>1 mm and D≦125 mm,        d/D ballasts, where d>25 mm and D≦50 mm,        
with d and D as defined in this standard.
Such fillers may include ultra-fines which are defined as fillers having a median diameter less than or equal to 20 m measured by means of a Cilas™ 850 or Sedigraph™ 5100 type granulometer (selected according to the granulometry of the filler to be measured). Examples of fillers are, for example, blast furnace cast vitrified slags, fly ash and other additions of silica of high fineness, or calcareous additions such as calcium carbonate.
The incorporation, in cement matrices or hydraulic binders, of fumed silica or siliceous additions, or calcareous additions such as calcium carbonate, is also known. In particular, it is known that calcium carbonate may be used, either as a dispersion in water, or in an aqueous medium without dispersant.
In particular, WO 99/47468 describes the use of calcium carbonate in the form of an aqueous dispersion for preparing concretes. This document is an example of preparing a concrete having a more or less acceptable compromise between ease of handling and resistance to premature aging. However, WO 99/47468 only describes incorporating a dispersant as a liquefier for improving fluidity, which is akin to the known functions of additives in the prior art.
EP 0 271 435, EP 0 725 043 and U.S. Pat No. 5,614,017 describe the use of plasticizers in cements, which improve the compressive strength, or reduce shrinkage, or increase the workability time, measured with an Abrams cone, also referred to as “slump”. In EP 0 271 435, the additive acts as a water reducer, which is perfectly in accord with the desirability of having a water/cement (W/C) ratio which is as low as possible in order to improve mechanical strength. In EP 0 725 043, the plasticizer is used at a very low concentration and the technical problem posed is completely different from that of the present invention, and as in U.S. Pat. No. 5,614,017. In the three cases, the aggregate is of the 0/D filler type (as defined above), the calcium carbonate is used as a dry powder rather than in dispersion, and the addition of the admixture is effected at the time of preparation of the concrete, that is to say subsequent to, rather than before the preparation of the concrete.
It is also known that admixtures can be used for deflocculating the cement paste and/or reducing the quantity of water in the cement. In this regard, it is known that if the proportion of water increases in a cement matrix or hydraulic binder, the mechanical strength is reduced. One of skill in the art, therefore, always endeavours, in their formulations, to reduce the water/cement ratio (W/C). However, one of skill in the art also knows that, if the proportion of water increases in a cement matrix or hydraulic binder, the workability thereof (that is to say its ability to be handled, pumped, etc) increases. Thus, one of skill in the art is therefore very often forced to seek a compromise between the mechanical properties and workability of such cement matrices or hydraulic binders.
One of the most important mechanical properties of cement matrices or hydraulic binders, for one of skill in the art, concerns the “strength at young ages” of the cement matrix or hydraulic binder. This property is defined as the change in the compressive strength curve, according to the age of preparation of the cement matrix or hydraulic binder, in the region of from 0 hours to 7 days following the preparation of the cement matrix or hydraulic binder. Normally, a measurement is made at 2 days and 7 days.
As discussed above, there is an important and recognised need for significantly increasing the strength at young ages property, without negatively affecting other advantageous properties, such as for example workability.